A vehicle has been widely known, which has an automated manual transmission (hereinafter, referred to as AMT) that is structurally based upon a manual transmission (hereinafter, referred to as MT) and is adjusted to establish a shift stage in the MT at an appropriate shifting condition by a computer control, thereby enabling to improve fuel consumption. This type of vehicle further has a position sensor for detecting an operating position of the shift lever, and an electronic control unit for controlling a shift operation in response to a signal automatically outputted or manually outputted. The electronic control unit has a shift lever operating position-judging device for judging an operating position of a shift lever based upon a signal outputted from a position sensor.
The shift lever is selectively placed at plural positions such as a backward drive position “R”, a neutral position “N”, an automated shift position “D” and a manual shift position “M”. The position sensor is constructed with plural switches turned ON upon the shifting operation of the shift lever to each position. The switch turned ON is employed as a parameter for judging the current position of the shift lever. When at least one of the switches of the shift lever position sensor malfunctions, the shift lever position may not be able to be recognized correctly. In light of foregoing, following devices have been well known, one of which is capable of detecting the shift lever position regardless of the shift lever position sensor failure, while the other one of which is capable of detecting the shift lever position sensor failure.
As a first example of the above, Japanese Patent No. 3419328 discloses a shift lever operating position detecting device, which is provided with four ON-OFF switches SW1, SW2, SW3 and SW4. Combined ON-OFF operations of the ON-OFF switches SW1, SW2, SW3 and SW4 exhibits to which operating position the shift lever had been shifted. There are five operating positions, namely, a reverse drive position “R”, a neutral position “W”, a forward-shift position “S”, a shift-up position “+” and a shift-down position “−”. Each ON-OFF switch outputs a switch signal of which signal level is opposite and a check signal. According to the disclosure, the actually malfunctioned ON-OFF switch can be identified. Further, the remaining three switches can identify the current shift position of the shift lever at least among the reverse drive position “R”, the neutral position “N” and the forward-shift position “S”.
As a second example of the above, Japanese Utility Model Application Publication No. 05(1993)-90029 discloses a shift lever position sensor failure judging device, which judges the failure of the shift lever position sensor in response to a signal outputted from the position sensor during the shifting operation.
In order to detect the failure of the ON-OFF switch provided in the shift lever operating position detecting device disclosed in the Japanese Patent No. 3419328, the device includes a first failure judging means for individually judging the failure of each ON-OFF switch based upon first and second signals outputted from each ON-OFF switch. The first failure judging means includes a first switch and a second switch. The first switch is placed in an ON state when the shift lever has shifted to a predetermined position and in an OFF state when the shift lever has shifted to any other position except for the predetermined position. The second switch is placed in an OFF state when the first switch is placed in the ON state, while is placed in an ON state when the first switch is placed in the OFF state. Namely, the first failure judging means is configured with two groups of switches, and so the number of switches may be increased.
In the shift lever position sensor failure judging device disclosed in the Japanese Utility Model Application Publication No. 05(1993)-90029, the failure is detected in response to the signal condition of each operating position of the shift lever. Therefore, the switch failure can not be detected at both ends of the operating position.
A need exists for providing a shift lever operating position judging device capable of judging a shift lever position by combinations of the less number of switches. A need further exists for providing a shift lever operating position judging device capable of judging a shift lever position and judging a failure by combinations of the less number of switches.